HMC7044 Datasheet, PDF (36/72 Pages) Analog Devices – JESD204B clock generation

HMC7044
RF_SYNC OR PLL2 SYNC
RESET
SYNC
SETUP
PULSE
GENERATOR
SETUP
NOTIFY CHANNEL FSM
WHAT TYPE OF EVENT
IS COMING
SYNC
REQUEST
CLEAR
WAIT
STARTUP
PULSE
GENERATOR
TIMEOUT?
POWER DIVIDERS/SYNC BLOCKS,
PAUSE BLOCKS, RESET LATCHES
REMOVE LATCH RESET,
PREPARE TO START CLOCKS
START CLOCKS,
WITH CLEAN TIMING,
SMALL PIPELINE DELAY
WAIT UNTIL THE NUMBER OF
PULSE GENERATOR CYCLES
EXPIRES
DONE
REMOVE POWER
PULSE
GENERATOR
REQUEST
Figure 45. Synchronization FSM Flowchart
FSM STATE
STARTUP PULSE GENERATOR = 2
DONE
DIVIDER CHANNEL
IF MUTE SIGNAL ARRIVES QUICKLY
RELATIVE TO SIGNAL TRAIN,
FIXED NUMBER OF VCO CYCLES
NO RUNT PULSE
FROM STATE CHANGE TO STARTUP, AND
ANY INTENTIONAL DIGITAL/ANALOG OFFSET
Data Sheet
FSM STATE
STARTUP PULSE GENERATOR = 2
DONE
DIVIDER CHANNEL
IF CONTROL IS TOO LATE
RELATIVE TO SIGNAL TRAIN,
THERE IS A RUNT PULSE
Figure 46. Start-Up Behavior of an Example Divider Configured as a Pulse Generator
Clock Grouping, Skew, and Crosstalk
Although the output channels are logically independent, for
physical reasons, they are first grouped into pairs called clock
groups. Each clock group shares a reference, an input buffer,
and a sync retime flip flop originating from the VCO
distribution network.
The second level of grouping is according to the supply pin.
Clock Group 1 (Channel 2 and Channel 3) are on an independ-
ent supply, and the other supply pins are each responsible for
two clock groups.
As the output channels are more tightly coupled (by sharing a
clock group, or by sharing a supply pin), the skew is minimized.
However, the isolation between those channels suffers. Table 20
shows the clock grouping, and Table 21 show the typical skew
and isolation that can be expected and how it scales with distance
between output channels.
Isolation improves as either the aggressor or affected frequencies
decreases. Nevertheless, for particularly important clock channels
where spurious tones must be minimized, carefully consider
their frequency and channel configurations to isolate continu-
ously running frequencies onto different supply domains.
Channels configured as pulse generators are normally not an
issue, because they are disabled during normal operation.
Rev. B | Page 36 of 72